1. Technical Field
Several aspects of the present invention relates to a transistor, a transistor circuit, an electrooptical device and an electronic apparatus.
2. Related Art
In recent years, development of a thin film transistor using an organic material (organic semiconductor material) that has an electric conducting property like semiconductor has been studied. Such thin film transistor has advantages such that it can be suitably adopted for thinner and lighter electronic devices, it has flexibility and its material cost is inexpensive. For these advantages, the thin film transistor made of an organic material is expected to be used as a switching element for a flexible display or the like.
Two types of structure have been proposed for such thin film transistor. One is a top gate structure in which a source electrode, a drain electrode and an organic semiconductor layer are formed on a substrate and a gate insulating layer and a gate electrode are sequentially formed on top of them. The other is a bottom gate structure in which a gate electrode and a gate insulating layer are firstly formed in this order on a substrate and then a source electrode, a drain electrode and an organic semiconductor layer are formed on top of them.
An organic semiconductor has a disadvantage that it has a small on-state current compared with that of an inorganic semiconductor. JP-A-2005-079549 is an example of related art. The example proposes an organic thin film transistor having two gate electrodes. In the organic thin film transistor according to the example, two channels are formed because the two gate electrodes are provided there and it is possible to control a larger current compared to the case where only a single gate electrode is provided.
However, the two channels formed in the organic thin film transistor according to the example has the same carrier polarity so that the organic thin film transistor has a small freedom when it comes to designing a circuit in which organic thin film transistors are combined.
Moreover, in the case of an organic semiconductor, it is difficult to control its threshold voltage and channel polarity by controlling impurity doping which is normally performed in the manufacturing process of a transistor made of amorphous silicon or polysilicon. For this reason, it is not easy to overcome the above-mentioned disadvantage.